The ancient seers of India realized the highest non-dual Truth and thus attained to unity in the religious field; they succeeded in bringing religion to the rank of a perfect and complete science. The methods adopted by them to come to this result were the same as those followed by all the sciences of the present day. This book discusses how the philosophers of India applied these rational methods in coming to their respective discoveries, thus establishing the scientific character of Indian philosophy and religion. The book chiefly makes a comparative study of Samkhya, Vedanta and other systems of thought.